Newly purchused item

I bought my sister a wireless earphone set for Xmas on 9th December. When she opened it on Xmas day to install it it did not work I then try to exchange it at Dion Wire the day after Xmas at Woodmead i was told it had to be returned 7 days after purchase I was never informed about that at the time of purchase I insist to be supp**** with new set due to lack of informing me.